1. Field of the Invention
The present invention, in general relates to backup battery monitoring devices and, more particularly, to devices and methods for determining the state of a backup battery.
Backup batteries are used for a variety of purposes. An important application involves the use of an uninterruptible power supply (or system), sometimes also known by the acronym "UPS".
An uninterruptible power supply may require many batteries to be placed in series to supply the necessary voltage and current. Such placement of a group of batteries in series is referred to as a battery "string". Additional battery "strings" may also be arranged in parallel so as to provide added backup time in the event of a power failure or to provide a fail-safe level of redundancy.
It is well known that if one of the batteries should fail, in particular if it should fail by developing an electrical open, then the uninterruptible power supply cannot function in the event of a loss of primary electrical power (if only one string is present). At a minimum, backup time will be reduced. This is also true if the failure involves a short occurring within one of the batteries.
As a result, periodic labor-intensive testing is done to verify the condition of the backup batteries. Alternatively, circuits have been invented to measure the status of the backup batteries, but these have proven either to be expensive to purchase, difficult to install, or marginal in performance.
Accordingly there exists today a need for an apparatus and method that is inexpensive, easy to install, and effective at determining the status of backup batteries.
Clearly, such an apparatus and method is a useful and desirable.
2. Description of Prior Art
Battery verification devices are, in general, known. For example, the following patents describe various types of these devices:
U.S. Pat. No. 4,138,670 to Schneider et al, Feb. 6, 1979;
U.S. Pat. No. 4,316,133 to Locke, Jr., Feb. 16, 1982;
U.S. Pat. No. 4,441,066 to Burnenko, Apr. 3, 1984;
U.S. Pat. No. 4,618,857 to Dubois et al, Oct. 21, 1986;
U.S. Pat. No. 4,820,965 to Siemer, Apr. 11, 1989;
U.S. Pat. No. 4,929,931 to McCuen, May 29, 1990;
U.S. Pat. No. 5,047,961 to Simonsen, Sep. 10, 1991;
U.S. Pat. No. 5,457,377 to Jonsson, Oct. 10, 1995; and
U.S. Pat. No. 5,744,932 to Kissel, Apr. 28, 1998.
While the structural arrangements of the above described devices, at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.